The need for more energy-efficient lighting is well known. A significant fraction of the electrical power consumed in the United States is for outdoor lighting, usually for outdoor commercial and municipal lighting, notably street lighting. Reducing demand for electrical power has become important, both for conservation of resources and reduction of energy cost.
There are well-known energy-efficiency and maintenance cost issues with conventional incandescent street lighting technologies. In addition, most outdoor commercial lighting technology uses a single light source per luminaire. When the bulb is energized, light radiates in all directions. Reflectors can be used to redirect the light, however, that approach introduces undesirable losses. In addition, for different applications, different patterns of illumination may be desired. For example, in some locations it is desirable to have light emitted in all directions, while in other locations, e.g. next to a window, emitting light in all directions may be undesirable. Providing multiple types of fixtures and multiple reflectors for various locations adds to the cost of maintenance, installation and inventory.
Light emitting diode (LED) technology has progressed substantially in the last few years. The assignee here provides high-brightness white LEDs for use in commercial outdoor lighting, as well as for other applications.
One approach to reducing the cost of changing from conventional incandescent to LED lighting technology in commercial lighting applications is to retrofit existing lighting fixtures (or luminaires) by replacing the light source portion of the luminaire with an LED light source. In this approach, the bulb, reflector, socket, and associated equipment are removed from the fixture. LED light engines mounted on custom sheet metal can then be placed inside the luminaire.
While this is method reduces the direct energy costs, it still suffers from the need for expensive customization to achieve desired light distribution patterns and illumination levels. In addition the light output is limited by the ability of the customized mounting structures to dissipate heat from the LEDs. The number and type of LEDs required for enough light to replace 200 watt and larger incandescent bulbs creates sufficient heat that careful further customization is required to maintain the temperatures necessary for longer life of the LEDs themselves. As a result almost every retrofit becomes a custom design, undesirably raising its costs, and thereby lengthening the “payback” period of the investment.